The invention relates to a spinning device of a rotor spinning machine comprising a spinning rotor made of magnetically conducting material, seated for rotation in an air chamber connected with an underpressure source, and having a stator comprising at least two electromagnetic coils and arranged around the outer circumferential surface of the spinning rotor.
DOS 24 33 712 discloses a device for mounting and driving a disk-shaped spinning rotor of a rotor spinning machine n which the spinning rotor consists of a circumferential wall and of the bottom of the spinning rotor, the inner side of the circumferential wall being provided with a slide wall and a collecting groove for collecting fibres into a fibre band to be twisted into the yarn during the spinning process. The bottom of the spinning rotor is full and flat, and its lower surface serves as one part of an aerostatic or aerodynamic bearing for taking up axial forces. The spinning rotor is surrounded by an electromagnetic unit comprising electromagnetic coils arranged in the stator common to them and serving chiefly for transmitting radial force. Opposite the bottom of the spinning rotor is arranged an inlet aperture through which in a well-known manner the fibres are fed into the spinning rotor and the spun yarn is led away. The spinning rotor is made of a ferromagnetic material.
The drawback of this solution consists in the difficult cooling of the spinning rotor, in particular when spinning manmade fibres at a speed exceeding 60,000 RPM where high temperature of the collecting surface of the spinning rotor is produced by mechanical losses. Since the spinning rotor makes a compact entity with its drive unit and the heat enters the spinning rotor immediately from the area where it is generated, the cooling of such spinning rotor leaves much to be desired since it is produced merely by the situating of the spinning rotor in the underpressure chamber used to produce underpressure in the spinning rotor.
To do away with the drawbacks of this solution, CZ 214 535, fitted with the spinning rotor of the same design as that of DE 24 33 712, has introduced a heat insulation separating at least the collecting groove area of the spinning rotor from the drive device surrounding the spinning rotor and producing the heat energy. Said heat insulation can consist either of an air gap or of an elastic body.
The spinning rotor revealed in CZ 214 535 is a considerably complicated solution both in design and before all in its actual production process. Its efficacy is subject to doubt, especially in the spinning of man-made fibres involving considerable heat generation due to the friction of said fibres against the inner surfaces of the spinning rotor. No solution is provided for the removal of such heat; on the contrary, its removal is hampered by said insulation layer: For this reason, this solution has never been applied on rotor spinning machines and is only one of the deadlocks in the development of the spinning rotors.
The solution described in DE 24 33 712 has undergone further development in which has been maintained the dish shape of the spinning rotor with the flat bottom situated opposite the inlet aperture. The spinning rotor is situated in an underpressure chamber and contains no air vents. Also maintained has been the seating of the spinning rotor by means of its bottom on an. air cushion even if the embodiment proper of the aerostatic or aerodynamic bearing has undergone modifications in the course of its development. The drive coils have been moved from the area around the circumference of the spinning rotor under the bottom of the spinning rotor, for instance in DE 43 42 583 in which the dish-shaped spinning rotor is made of a non-magnetic material such as aluminium. In the bottom of the spinning rotor are situated drive magnets and guide magnets separated from each other by a non-magnetic substance filling out the space between them. This solution permits a multi-sector pair arrangement of the drive magnets and also a concentric arrangement of the guide magnets.
A drawback common to all the above mentioned solutions consists in the dish-shaped spinning rotor with full bottom situated in the underpressure chamber because the technological air, in the course of the spinning process, enters the spinning rotor with the fibres through the inlet aperture and is at the same time led out through the same inlet aperture. In addition to the fibre feed, said inlet aperture houses also a draw-off trumpet for delivering the spun yarn. Since the increasing rotation speed of the spinning rotors is accompanied by the reduction of their diameters and, consequently, by the reduction of the diameter of the inlet aperture of such high-speed rotors, it is very difficult to position said devices opposite the inlet aperture.
Another drawback consists in the complicatedness, both in design and in production, of the bottom of the spinning rotors which must be fitted with recesses for the drive, and guide magnets and with one part of the aerostatic bearing. The position of the magnets, when inserted in said recesses, must be exact. At the same time must be maintained the static and dynamic balancing of the spinning rotor. Said facts considerably increase the purchase price of the spinning rotor. However, even with increased service life, the spinning rotors are a machine part subject to frequent replacement so that the high purchasing price is a considerable cost item for the user of the spinning machine.
The above drawbacks of the state of art are eliminated or reduced by a spinning device according to the invention whose principle consists in that the spinning rotor is made as a ring magnetized normal to the plane passing through the axis of the spinning rotor.
The chief advantage of this solution consists in the fact that the spinning rotor contains only a minimum quantity of material, and more exactly, only such quantity as is necessary for the creation of the functional surfaces of the spinning rotor, i.e., of the fibre slide surface and of the collecting groove. This reduces considerably the spinning rotor mass and, consequently, the energy amount needed both to start and to brake the spinning rotor.
At the same time it becomes superfluous to have the spinning rotor shaft, and the bearing for seating the spinning rotor which not only further reduces the mass of the rotating system but also saves energy by eliminating the friction losses in the bearing.
As compared with the spinning rotors seated in an aerostatic and/or aerodynamic bearing, the solution according to the present invention, in addition to the above reduction of the mass achieved by the elimination of the spinning rotor bottom, also saves energy otherwise needed for the function of such aerostatic and/or aerodynamic bearing.
In its narrowest sections, the inner side of the spinning rotor defines the inlet aperture and the outlet aperture, of the spinning rotor, and an air chamber is connected to an underpressure source behind the outlet aperture of the spinning rotor.
This arrangement ensures the movement of the technological air through the spinning rotor from the inlet aperture to the outlet aperture, i.e., in the direction identical with that of the singled-out fibres led in a well-known manner into the inlet aperture of the spinning rotor. Such advantage has been up to now known in spinning rotors fitted with air vents in which the underpressure is generated by their proper rotation. Besides, the arrangement according to the invention eliminates the influence of the rotation speed of the spinning rotor on the underpressure in the spinning rotor, which is the chief drawback of the spinning rotors fitted with the air vents and at the same time the chief advantage of the spinning rotors seated in an underpressure air chamber in which the air stream is generated by the connection of the air chamber to an external underpressure source, the drawback of these spinning rotors consisting in that the technological air does not at all pass through the inner space of the spinning rotor.
It results from the above that the spinning device according to the invention, among other things, combines the advantages, and eliminates the drawbacks, of the two well-known spinning rotor designs.
In a preferred embodiment of the spinning device according to the invention, the outlet aperture of the spinning rotor houses a draw-off trumpet which can be preferably introduced through the inlet aperture of the spinning rotor into the inner space of the spinning rotor.
In another embodiment, the draw-off trumpet of the yarn is seated in an air chamber behind the outlet aperture of the spinning rotor. Thus, the draw-off trumpet can be seated in an optimum position in relation to the collecting groove of the spinning rotor according to the material and to the required properties of the yarn to be produced.
The top optimation for various yam sorts can be achieved by mounting the draw-off trumpet adiustably in axial direction. As regards the relation Lo the draw-off Trumpet, the diameter of the outlet aperture of the spinning rotor is preferably superior to the maximum outer diameter of the draw-off trumpet for ensuring the stream of the technological air through the spinning rotor from the inlet aperture to the outlet aperture.
The outer circumferential wall of the spinning rotor is surrounded by a part of the body of the stator of a synchronous electric machine in which the pole extensions of the electromagnetic coils of the stator are seated. The electromagnetic coils can be seated either outside the area around the circumference of the spinning rotor which simplifies the design of the spinning device, or in the area around the circumference of the spinning rotor as is the case in the example of embodiment shown and described later which, in turn. spimplifies the design of the stator.
The electromagnetic coils are preferably connected with a frequency converter of an integrated control system of the spinning device comprising a control circuit with means for interrupting the power supply to a feed clutch with information inputs to which there are connected yarn quality and presence sensors. This provides for the control of the spinning rotor in accordance with the specific conditions existing at the operating unit in question.
In particular for monitoring the spinning rotor position, it is advantageous to place at least three sensors of the magnetic field around the outer circumference of the spinning rotor, preferably in the stator between the pole extensions, and more preferably still, evenly.
The magnetic field sensors are connected to the information inputs of the control circuit of the integrated control system so that their information influences the spinning rotor together with the other items of information at the disposal of the control circuit, thus ensuring optimized run and position of the spinning rotor both during the spinning and during the start and stop motion.
To prevent the spinning rotor from getting damaged by accidental contact with the stator during the start or stop motion, the outer surfaces of the spinning rotor and/or the inner surfaces of that stator part which contains the pole extensions are coated with a protective coating consisting for instance of rubber or of a plastic material.